Observation of Supramolecular Chirality in a Hierarchically Self-Assembled Mixed-Stack Charge-Transfer Complex

Supramolecular chirality was observed in a charge-transfer (CT) complex formed by self-assembly of beta-cyclodextrin-linked pyrene and adamantane-linked pyromellitic diimide in water. In the complex, the pyrene-pyromellitic diimide CT interaction is reinforced several-fold by the strong beta-cyclodextrin-adamantane inclusion binding interaction, as confirmed by H-1 NMR, absorption, fluorescence and isothermal titration calorimetry studies. The CT complex exhibited high stability, as inferred from the temperature-de-pendent absorption and NMR studies. The CT absorption band exhibited a positive Cotton effect indicative of supramolecular chirality for the complex. Twisted fibres were observed in TEM, AFM, and SEM experiments. A mechanism involving synergistic binding interactions leading to 2D sheets, followed by twisting of the sheet, is proposed for the formation of twisted fibres. This system offers a chance to investigate a combination of supramolecular CT and supramolecular chirality and explore their synergistic effects.